DESCRIPTION: The proposal has 2 broad goals. The first goal is to elucidate the mechanisms by which neurotrophin interactions with trk and 75kDa neurotrophin receptors (p75NTR) convey retrograde axonal signals to the neuronal cell body. The second goal is to characterize the signal transduction pathways by which p75NTR regulates cell migration and cell death. To test the hypothesis that NGF induces internalization of the NGF/trkA complexes at the axon terminus and transports this endosomal complex back to the neuronal cell body leading to activation of the MAP kinase pathway and other signaling pathways, axonal transport of various components of the NGF signal transduction pathway will be examined in which embryo dorsal root ganglion sensory neurons in compartmentalize cultures (Campenot Chambers). Neuronal differentiated mouse P19 embryonic carcinoma cells, embryonic stem cells (ES) and PC12 cells will be employed to test the hypothesis that neurotrophin/p75NTR enhances apoptotic death of neuronal and other cell types, and to determine whether the NF-KB signaling pathway participate in this regulation. In addition, to test the hypothesis that a major functional ligand of the p75NTR remains to be discovered, the soluble ectodomain of the p75NTR will be used as an affinity probe to extract ligands from tissue extracts, to localize ligands in tissue sections and to screen cDNA libraries expressed in mammalian cells.